Collapsible canopy framework

ABSTRACT

A structure that is foldable and expandable to support a canopy when a covering is placed on top of the framework includes a plurality of upright supports and a plurality of edge scissor assemblies that interconnect adjacent ones of the upright supports. Mounting brackets are disposed on the upright supports and also between scissor assemblies to fasten outer, end portions of the edge scissor assemblies together or to the upright supports. The mounting brackets each have a plurality of unique single side wall sockets each including a means for limiting torsional twisting of the scissor assemblies fastened in the socket. The limiting means comprises a complementary groove or rib for matingly engaging, in a complementary fashion, a complementary rib or groove, respectively, formed on the end of the scissor member received in the socket and secured therein with a pivot pin. The mounting brackets on each upright support may be relatively movable to allow expansion and contraction of the framework while limiting the side to side stresses on the scissor members pivotally held within the mounting brackets.

BACKGROUND

1. Field

The present disclosure generally relates to the attachment of pivoting structural members in an integrated collapsible canopy system. Specifically, the present disclosure relates to a structural device, in the form of non-compressible mounting brackets each forming a plurality of sockets for use in a collapsible canopy framework, wherein each socket captures an end portion of a scissor assembly member.

2. General Background

There is a need recognized when collapsible canopy products are manufactured to simplify the mounting bracketing of the scissor bar elements, one to another into scissor units and the resulting scissor units into interconnected scissor or truss assemblies, and in the connection of such truss assemblies in a pivotal expandable/collapsible manner to respective corner and intermediate supports. There is a need for interconnections which would be more resistive to shear and bending moments. The mounting brackets in the following description are structured to provide free pivots while at the same time resisting lateral and torsional deflection of the scissor assembly components.

SUMMARY

A collapsible frame adapted to support a flexible fabric canopy or tent in an extended configuration and a collapsed configuration in accordance with the present disclosure has a plurality of upright support members oriented alongside one another in the collapsed state and movable outwardly apart from one another toward the expanded state. A plurality of edge scissor link assemblies each interconnect adjacent support members, each edge scissor link assembly comprising one or more pairs of scissor link members.

A unique mounting bracket connects one or more scissor link members to one of either one of the upright support members or another edge scissor link assembly. The mounting bracket is a solid body having a plurality of sockets therein each shaped to receive and pivotally hold one end of one of the link members therein. Each socket has an inner face, a horizontal wall, and only a single vertical side wall merging substantially at a right angle with the horizontal wall and the inner face of the socket. A pivot fastener extends through the one end of the link member and into the single side wall to hold the member in the socket and permit rotation of the link member about an axis of the pivot fastener. The mounting bracket further includes means formed between the horizontal wall of the socket and the end of the link member in the socket for limiting the effect of twisting side stresses applied to the scissor link member in the socket when the frame is fully expanded to support the canopy or tent cover.

The means for limiting preferably is formed within the socket by a groove formed in the horizontal wall extending parallel to the vertical wall and mates with a complementary shaped rib formed on the end of the scissor member engaged with the groove in the socket when the pivot fastener fastens the link member to the vertical wall in the socket.

Alternatively, the means for limiting may preferably be a rib formed in the horizontal wall extending into the socket parallel to the vertical wall and a complementary shaped groove formed on the end of the scissor member engaged with the rib in the socket when the pivot fastener fastens the link member to the vertical wall in the socket.

The framework structure includes several different configurations of the mounting bracket of the present disclosure that have two, three, or four or more sockets formed therein, each of which includes the means for limiting the effect of twist or side stresses to which the scissor member in the socket may be subjected to. For example, a mounting bracket at one of the corners of the framework may have two sockets at right angles. A mounting bracket placed in the center of the framework for supporting the central portion of the canopy roof will have four sockets at right angles from each other. If the canopy or tent framework has roof members extending from the corners, then the corner mounting brackets each may include a socket oriented between the right angle sockets.

The framework structure can be folded and stored in a collapsed state and erected in an expanded state on a support surface in order to support a canopy covering above the support surface. In the collapsed state, the support members are oriented alongside one another but are movable outwardly apart from one another towards the expanded state.

A preferred embodiment of the framework structure includes a plurality of edge scissor assemblies that form truss members for the expandable framework with there being an edge scissor assembly interconnecting adjacent ones of the support members. Each edge scissor assembly may be made of two or more pairs of scissor members linked together. In addition, mounting brackets in accordance with the present disclosure connecting the scissor member pairs together. In addition, a fixed and slidable pair of mounting brackets are disposed on the upright support members to fasten the edge scissor assemblies to the upright support members.

The mounting brackets each have sockets that include a track or means for engaging the end of the scissor member of the scissor assembly received within a respective one of the sockets. A fastening pivot pin pivotally secures each outer end portion of each edge scissor assembly in its respective socket.

The mounting brackets on the upright support member are relatively movable with respect to one another so that the edge scissor assemblies are operative to open and close whereby the framework structure may move between the expanded and contracted states. One mounting bracket is stationary while the other is slidable. The sockets and the mounting brackets thus provide pivotal connections for the scissor bars or members which form the scissor pairs which in turn comprise the scissor assemblies.

The roof support assembly of the framework may be extendible roof members pivotally attached to the stationary mounting brackets in sockets at upper ends of the upright support members with these roof members projecting radially inwardly to form one or more apices to support the canopy covering. Alternately, the roof support members may extend radially inwardly from the slide mounting brackets to form such apex.

These and other objects of the present disclosure will become more readily appreciated and understood from a consideration of the following detailed description of an exemplary embodiment when taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary canopy framework structure of the present disclosure;

FIG. 2 is a perspective view of a corner mounting bracket at an upper end portion of a corner support member;

FIG. 3 is a perspective view of an exemplary slide mounting bracket of the present disclosure for use on a corner support member;

FIG. 4 is a perspective bottom view of a floating apex mounting bracket as shown in the exemplary embodiment of the present disclosure in FIG. 1;

FIG. 5 is a perspective bottom view of the lower floating mounting bracket shown in FIG. 1;

FIG. 6 is a perspective view of an exemplary floating mounting bracket of the present disclosure used to connect adjacent scissor units;

FIG. 7 is a partial vertical sectional view through an assembled scissor member and socket of an exemplary mounting bracket of the disclosure such as in FIG. 3.

FIG. 8 is a perspective view of an alternative embodiment of the slide mounting bracket shown in FIG. 3 illustrating an alternative groove and rib arrangement in accordance with the disclosure.

FIG. 9 is a bottom perspective view of the top corner mounting bracket shown in FIG. 2.

FIG. 10 is a separate perspective view of an exemplary scissor bar member showing the end cap structure that matingly fits within one of the sockets in the mounting brackets shown in FIG. 9.

FIG. 11 is a sectional end view of an alternative embodiment of a socket as in FIG. 7.

FIG. 12 is a sectional end view of a different embodiment of a unit of FIG. 6.

DETAILED DESCRIPTION

The present disclosure specifically concerns novel mounting brackets which may be used to interconnect the framework forming elements, such as the upright corner and intermediate leg support members, scissor assemblies and roof support structures in a collapsible canopy framework structure. FIG. 1 shows a perspective view of a framework structure 11 used to support a fabric canopy 12. In FIG. 1 a framework structure 11 is shown in an expanded state and supports a covering fabric 12 (shown in partial phantom view) to produce a canopy unit 10. Framework structure 11 is formed by four upright corner support members 14 each of which comprises a pair of telescoping pole structures such as square tubular upper leg section 15 into which square tubular lower leg section 16 is slidable received. Each upright support member 14 has a lower end 17 which engages or rests on a support surface, such as the ground, and an upper end 18 opposite the lower end 17.

A stationary mounting bracket 60 in an exemplary embodiment of the framework 11 of the present disclosure is disposed at each upper end 18. A sliding mounting bracket 62 is slidably received on upper leg section 15 so that each slide mounting bracket 62 may move from a position remote from a respective stationary mounting bracket 15 to a location proximate stationary mounting bracket 60 in the fully expanded state as shown in FIG. 1. When located proximate to stationary mounting bracket 60, each mounting bracket 62 may be latched into position by a suitable latch structure. This can be a spring mounting bracketed button latch 13 a in the floating mounting bracket 62 and is engagement when exposed so that it enters into holes 13 b in the respective walls of support 15. Each upright support member 14 is interconnected to an adjacent upright corner support member by a scissor assembly 19 which has opposite outer upper and lower ends captured in sockets formed in mounting brackets 60 and 62. In an additional aspect, visible in FIG. 3, the spring-loaded pull-out pin 13 a is pulled by means of the pull ring 13 c. A spring biases the pins 13 a towards insertion into the apertures 13 b.

In FIG. 1, the peripheral edge scissor assemblies 19 each comprise a set of two pairs of scissor member bars 40 and 42. It should be understood that additional pairs of scissor members 40 and 42 may be utilized in forming larger canopy or tent framework structures. Each of scissor bars 40 and 42 is preferably hollow, extruded aluminum tubular material having a rectangular cross section and substantially similar to one another. Each bar may also have internal strengthening ribs to provide enhanced rigidity. Alternately, scissor bars 40 and 42 may be made of any suitable construction material such as steel, plastic, fiberglass and the like. For example, the scissor bars 40 and 42 have a hollow interior 70 formed by sidewalls 72 and 74. The sidewalls define a vertical dimension of height “h” for the scissor bar such as scissor bars while sidewalls 76 and 78 define a horizontal dimension or width “w.”

The scissor bars 40 and 42 are connected at common central pivot joint 43. A pivot fastener structure is provided. The pivot fastener structure includes a pair of cooperative mating pivot fastener structures that define a pivot axle that is a non-compressive element formed by a pair of cooperative axle pins such as female pin and male pin. The male pin has an elongated shaft terminating in a threaded end of reduced cross-section which, in turn, may be threadably received in threaded bore of shaft on the female pin. When joined, the shoulder on the shaft abuts the rim on the shaft so that the respective heads of female and male axle pins have a minimum distance of separation defined by the lengths of shafts. The minimum distance for the spacing between heads is at least the combined cross-sectional widths of scissor bars 40 and 42. Further, the heads are preferably separated a minimum distance to accommodate a spacer washer. The heads are tapered, and countersunk washers are preferably provided for mounting bracketing on the outermost sides of scissor bars 40 and 42.

Mounting brackets 20 connect the scissor units 40 and 42, as shown in FIG. 1, one to another, in end-to-end relation in the form of either single or multiple scissor unit trusses to their respective upright supports 14. Each of the mounting brackets 20 has sockets 120 as described below with reference to the corner mounting brackets 60 and 62. One of these mounting brackets 20 is shown upside down in FIG. 6. In the embodiment of the framework 11 shown in FIG. 1, the mounting brackets 20 also have sockets 120 connecting ends of a scissor unit pair 40 and 42 between the edge scissor assembly 19 and the roof support mounting brackets 66 and 67 respectively. The roof support mounting brackets 66 and 67 are similar in structure to the corner mounting brackets 62 and 60 respectively, except that each of brackets 66 and 67 has four sockets as is shown in FIGS. 4 and 5.

A separate perspective upper view of a corner mounting bracket 60 is shown in FIG. 2 and a bottom view of this mounting bracket 60 is shown in FIG. 9. The stationary mounting bracket 60 is a solid body that has a central portion 112 having a cavity 114 formed therein. Cavity 114 is sized to matingly receive an upper end portion of an upright support member, such as a corner support member 14. A pair of flanges or lobes 116 and 118 extend outwardly from the central section 112 at right angles to one another to form the corner configuration. Each of lobes 116 and 118 forms a portion of a socket 120. Each socket 120 is defined by a single vertical sidewall 122, which extends at right angles from both central portion 112 and the horizontal wall or flange 116. Thus the socket 120 has only one vertical sidewall 122, a horizontal wall 116 and an inner surface formed by the exterior of the central portion 112. Note that the corner mounting brackets 60 and 62 only have two sockets 120. In contrast, roof support mounting brackets 66 and 67 each have four sockets 120 as shown in FIGS. 4 and 5.

Mounting brackets 20 each has three sockets 120 as shown in FIG. 1 and FIG. 6. Each socket 120 includes a groove 302 extending parallel to the vertical side wall 122 of the socket 120, and, as shown in both FIGS. 6 and 8, the horizontal wall 164 merges via a curved surface 308 into the central section of the bracket 60, 62 or 20 having a radius of curvature complementary to the radius of curvature of the end cap 44 on the scissor members 40 or 42.

A transverse pivot pin 140 pivotally fastens each end cap 44 of one of the scissor bar members 40 or 42 into the socket 120 through bore 45 in the end cap 44. Each pivot pin 140 is preferably threaded into and fixed into the vertical wall 122 of the socket 120. The end portions of the respective scissor bar members 40 and 42 are sized for close fitted mated engagement in the sockets 120 for relatively free pivotal motion therein. Due to this close fitted construction, each sidewall 122 forms a planar contact surface with its respective scissor bar 40 and 42 and, thus, resists lateral and torsional deflections of their respective scissor bars 40 and 42 along the planar contact surface of vertical wall 122.

However, stresses and torsional loads that are applied off axis to the pivot pin 140 are not restrained by the vertical wall 122. Accordingly a unique means for limiting torsional loads and side stresses is incorporated into each of the sockets 120 in each of the mounting brackets 60, 62, 66, 67, and 20. These features are clearly shown in detail in FIGS. 3 through 12. Basically, each socket 120 includes a complementary set of ribs and grooves formed between the end cap 44 of the bar members 40 or 42 and the horizontal walls 116 and 118. These complementary rib/groove formations interact when the pivot pin 140 secures the end cap of the members 40 or 42 securely in the socket 120 to prevent side loading and side stresses from unduly twisting the pivot pin 140, providing a secure rotatable yet rigid joint structure without the need for an opposite side wall parallel to the single side wall 122 of the socket 120.

One exemplary arrangement of the stress limiting means incorporated into each of the sockets 120 in the mounting bracket of the present disclosure is shown with reference to the lower sliding bracket 62 shown in FIG. 3 and in cross sectional view in FIG. 7. The structure for supporting the scissor member 40 in the socket 120 includes a raised rib 300 formed on the end cap 44 around the curved portion of the end cap 44. This protruding raised rib 300 engages a complementarily shaped groove 302 best seen in FIG. 7. As the scissor member 40 is rotated about the pivot pin 140 the end cap 44, the rib 300 rides within the groove 302 and hence the scissor member 40 (or 42) is prevented from twisting out of parallel alignment with the sidewall 122 by the interaction between the complementary structures. The rib 300 need only extend partially around the end cap 44 and need not extend completely around as is shown in FIG. 3. Similarly the groove 302 need not extend as far up the inner wall as shown. Since the torsional loading is primarily experienced only when the frame work 11 is fully extended as in FIG. 1, the complementary rib/groove arrangement need only engage in the fully extended position as shown in FIG. 3.

As illustrated in FIG. 11, a different configuration is shown where the rib 310 is illustrated as having a triangular cross section, which fits into a V shaped groove 312 in the flange or base 164 of the socket 120. In FIG. 12, a different configuration is shown where the end cap 304 is shown with a trapezoidal cross sectional groove 313 for mating with the trapezoidal raised rib 314 in the flange or base 164 of the socket 120.

In different configurations of the sockets 120 there can be different shapes of the interacting rib and groove arrangement than that illustrated. In FIG. 8, for example, the mounting bracket 62 is configured with a raised rib 302 in the flange 164 extending parallel to the vertical wall 170 or 316 which engages a complementary groove 314 formed in the end cap 44 or 304. Otherwise the mounting bracket 62 shown in FIG. 8 is identical to the bracket shown in FIG. 3.

At the front edge of the flange or base 164 forming the horizontal wall of each of the sockets 120 there is a transverse rib 318 which protrudes from the flange 164 and engages a mating transverse groove 320 in the end cap 44. These rib/groove combinations operate to stabilize the mounting or mooring of the scissor elements 40 and 42 within the mounting bracket sockets 120.

Exemplary corner slide mounting brackets 62 are shown in perspective views in FIGS. 3 and 8. Each has a central section 152 defining a square shaped passageway 154 extending therethrough. An upper leg section of an upright support member 14 may be telescopically received through passageway 154 so that slide mounting bracket 62 may readily slide thereon. A pair of lobes 156 and 158 project outwardly from the central section 152 at right angles to one another to form the horizontal walls of sockets 120. Each of lobes 156 and 158 has a vertical wall 170 extending upward from the horizontal wall 164 formed by the lobe 156 or 158. The vertical wall 170 merges into the central section 152. The merger between the central section 152 and the horizontal wall 164 of each of the lobes 156 and 158 is preferably curved complementary to the radius of the end cap 44 of the scissor member 40 (or 42). The vertical wall 170 is provided with a countersunk threaded bore 166 to receive and hold a pivot fastener 140 therein to secure the scissor member in the socket 120 as shown in FIG. 3.

FIGS. 4 and 5 show perspective views of roof support mounting brackets 66 and 67 respectively. The upper mounting bracket 66 has a central section 232 through which extends a passageway 234 sized to accommodate a roof apex spring loading elements such as a support post 100 shown in phantom lines. Central section 232 has a plurality of lobes 238 that project horizontally outwardly from central section 232 at right degree angles with respect to one another. Each lobe 238 forms the horizontal wall of a socket 240 that is also defined by a vertical side wall 241 that merges from the lobe 238 into the central section 232. Countersunk bores 246 are again provided in the vertical side wall 241 to receive a fastening pin 140 forming a pivotal axle for scissor bar elements, such as scissor bar elements 40 and 42 which may be matingly received in each of sockets 240.

Lower central mounting bracket 67, shown in FIG. 5, includes a central section 252 provided with a passageway 254 extending therethrough. A plurality of lobes 258 project outwardly from central section 252 and each forms a socket 260 that has a single vertical wall rising from the lobe 258 and merging with the central section 252, which is also the same general construction described with respect to stationary mounting bracket 60, slide mounting bracket 62. Each of the sockets 260 has a groove 302 (or rib as in FIG. 8) configured to mate with a complementary rib (or groove) in the end cap 44 or 304 on the scissor member 40 or 42 as above described.

The central mounting brackets 66 and 67 are substantially identical to the other mounting brackets described above. The central mounting brackets may be of a different configuration but will necessarily have at least one socket 240 for each roof member to be terminated thereto.

While the mounting bracket apparatus has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure need not be limited to the disclosed embodiments. For example, other configurations of the canopy are envisioned. Another embodiment may include only three upright corner support members or five or six corner support members. In such configurations, the angles between sockets 120 or 240 may be other than 90 degrees. However, the internal structure of each socket will be substantially the same, defined by a single vertical wall and a horizontal wall both merging into an inner surface of the central section of the mounting bracket. Each socket will also have a groove or rib extending along the horizontal wall, spaced from and parallel to the vertical wall for receiving a complementary rib or groove formed in the end portion of the support member that is carried within the socket. This disclosure is intended to cover various modifications and similar arrangements that will be readily apparent to those skilled in the art and are included within the spirit and scope of the claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures. 

1. In a collapsible frame adapted to support a flexible fabric canopy or tent, the frame having an extended configuration and a collapsed configuration, the frame having a plurality of upright support members oriented alongside one another in the collapsed state and movable outwardly apart from one another toward the expanded state and a plurality of edge scissor link assemblies each interconnecting adjacent support members, each edge scissor link assembly comprising one or more pairs of scissor link members, and a mounting bracket connecting one or more scissor link members to one of either one of the upright support members or another edge scissor link assembly, the mounting bracket comprising: a solid body having a plurality of sockets therein each shaped to receive and pivotally hold one end of one of the link members therein, each socket having an inner face, a horizontal wall, and only a single vertical side wall merging substantially at a right angle with the horizontal wall and the inner face of the socket; a pivot fastener extending through the one end of the link member and into the single side wall to hold the member in the socket and permit rotation of the link member about an axis of the pivot fastener; and means formed between the horizontal wall of the socket and the end of the link member in the socket for limiting effect of twisting side stresses applied to the scissor link member in the socket.
 2. The mounting bracket as claimed in claim 1 wherein one of a pair of mounting brackets on each upright support member is a stationary mounting bracket and another of the pair being a slide mounting bracket, the slide mounting bracket being slidably secured to the upright support member and movable between locations proximate to and remote from the stationary mounting bracket when the respective the edge scissor assembly opens and closes.
 3. The mounting bracket as claimed in claim 2 wherein the means for limiting comprises a groove formed in the horizontal wall extending parallel to the vertical wall and a complementary shaped rib formed on the end of the scissor member engaged with the groove in the socket when the pivot fastener fastens the link member to the vertical wall.
 4. The mounting bracket as claimed in claim 1 wherein the means for limiting comprises a rib formed in the horizontal wall extending parallel to the vertical wall and a complementary shaped groove formed on the end of the scissor member engaged with the rib in the socket when the pivot fastener fastens the link member to the vertical wall.
 5. The mounting bracket as claimed in claim 3 wherein the rib and the groove each has a complementary trapezoidal cross sectional shape.
 6. The mounting bracket as claimed in claim 4 wherein the rib and the groove each has a complementary trapezoidal cross sectional shape.
 7. The mounting bracket as claimed in claim 3 wherein the rib and the groove each has a complementary curved cross sectional shape.
 8. The mounting bracket as claimed in claim 3 wherein the solid body has at least two sockets at right angles to each other.
 9. An expandable and collapsible framework structure comprising: a plurality of upright support members each having a bottom end positionable on a support surface and a top end opposite the bottom end, the support members oriented alongside one another in the collapsed state and movable outwardly apart from one another toward the expanded state; a plurality of edge scissor assemblies with there being an edge scissor assembly interconnecting adjacent ones of the support members, each the edge scissor assembly having a pair of link members with outer upper ends and outer lower ends, the edge scissor assemblies operative to open and close whereby the framework structure may move between the expanded and contracted states; and a plurality of mounting brackets disposed on the upright supports and operative to fasten the edge scissor assemblies thereto, each bracket having at least two sockets each receiving an end of one of the link members of the scissor assemblies therein, each socket having an inner surface, only a single vertical side wall extending from the inner surface, and a horizontal wall extending at a right angle from the side wall, and a pivot pin fastening the end of the scissor assembly member in the socket to the vertical wall, wherein each socket comprises means formed between the horizontal wall of the socket and the end of the link member in the socket for limiting effect of twisting side stresses applied to the scissor link member in the socket.
 10. The structure as claimed in claim 9 wherein one of a pair of mounting brackets on each upright support member is a stationary mounting bracket and another of the pair being a slide mounting bracket, the slide mounting bracket being slidably secured to the upright support member and movable between locations proximate to and remote from the stationary mounting bracket when the respective the edge scissor assembly opens and closes.
 11. The structure as claimed in claim 10 wherein the means for limiting comprises a groove formed in the horizontal wall extending parallel to the vertical wall and a complementary shaped rib formed on the end of the scissor member engaged with the groove in the socket when the pivot fastener fastens the link member to the vertical wall.
 12. The structure as claimed in claim 9 wherein the means for limiting comprises a rib formed in the horizontal wall extending parallel to the vertical wall and a complementary shaped groove formed on the end of the scissor member engaging with the rib in the socket when the pivot fastener fastens the link member to the vertical wall of the mounting bracket.
 13. The structure as claimed in claim 11 wherein the rib and the groove each has a complementary trapezoidal cross sectional shape.
 14. The structure as claimed in claim 12 wherein the rib and the groove each has a complementary trapezoidal cross sectional shape.
 15. The structure as claimed in claim 11 wherein the rib and the groove each has a complementary curved cross sectional shape.
 16. The structure as claimed in claim 12 wherein the solid body has at least two sockets at right angles to each other.
 17. The structure as claimed in claim 9 wherein the solid body has a central passage therethrough receiving one of the upright support members therein.
 18. The structure as in claim 9 further comprising each scissor assembly comprising at least two pairs of scissor members connected together by mounting brackets wherein each mounting bracket has at least two sockets each receiving an end of one of the link members of the scissor member pairs therein, each socket having an inner surface, a single vertical side wall extending at a right angle from the inner surface of the socket, and a horizontal wall extending at a right angle from the single side wall, and a pivot pin fastening the end of the scissor member in the socket to the vertical wall, wherein each socket comprises means formed between the horizontal wall of the socket and the end of the link member in the socket for limiting effect of twisting side stresses applied to the scissor link member in the socket while the structure is in the expanded state.
 19. The structure as in claim 18 wherein the means for limiting comprises a groove formed in the horizontal wall extending parallel to the vertical wall and a complementary shaped rib formed on the end of the scissor member engaging with the groove in the socket when the pivot fastener fastens the link member to the vertical wall.
 20. The structure as claimed in claim 18 wherein the means for limiting comprises a rib formed in the horizontal wall extending parallel to the vertical wall and a complementary shaped groove formed on the end of the scissor member engaging with the rib in the socket when the pivot fastens the link member to the vertical wall of the mounting bracket. 